Recently, mobile broadband traffic has been exploding in wireless networks such as WCDMA (wideband code division multiple access). One consequence is a corresponding steep increase in interferences in these networks, or equivalently, a steep increase in load. This makes it important to exploit the load headroom that is left in the most efficient way.
Also, wireless networks are becoming more heterogeneous, with macro BSs (base station) being supported by low power BSs at traffic hot spots. Furthermore, home base stations are emerging in many networks. This trend puts increasing demands on inter-cell interference management.
In heterogeneous networks (HetNets), different kinds of cells are mixed. In a HetNet architecture, multiple low power cells can be embedded within a larger macro cell such as illustrated in FIG. 1. As seen, in the HetNet 100, a macro base station 110, which is a type of a radio node, is deployed and serves a corresponding macro cell 115. But in addition, several small (also referred to as “pico”) base stations 120, also a type of radio node, are deployed and serve corresponding small or pico cells 125. The transmission powers of these pico nodes 120 are relatively small compared to that of the macro node 110 (e.g., 2W vs. 40W).
HetNets can be divided into two deployment categories—co-channel and combined cell. In the co-channel deployment, the pico nodes have cell identifiers different from that of the macro node. That is, the pico nodes create pico cells with different ids from the overlapping macro cell. FIG. 1 illustrates a co-channel deployment example. As seen, the co-channel deployment 100 is such that the macro node 110 creates the macro cell 115 will cell ID “A”. The pico nodes 120-1, 120-2 and 120-3 create corresponding cells 125-1, 125-2 and 125-3 with cell IDs “B”, “C” and “D”. Note that the macro cell 115 overlaps each of the pico cells 125-1, 125-2 and 125-3.
But in the combined cell deployment, the pico node has a cell identifier same as that of the macro node. This is illustrated in FIG. 2. In the combined cell HetNet deployment 200, all radio nodes—the macro node 210 and the three pico nodes 220 all transmit the same cell ID “A”. Again, the macro cell 315 overlaps the pico cells 225.
A problem that arises in Hetnets in that the cells—macro and pico—are likely to have different radio properties in terms of radio sensitivity, frequency band, coverage, output power, capacity, and acceptable load level among others. An important factor in HetNets is that of the air interface load management, i.e., the issues associated with the scheduling of radio resources in different cells and the interaction between cells in terms of inter-cell interference.